Turns out Casio offers a handful of wristwatches with "10 year battery life". The claim is that thanks to "an advanced technology" the battery life in those watches is extended to ten years.
Now if you look at different models you see that they are rather complicated hence likely energy consuming - for example, AW-80-1AV model has both a liquid crystal display and hands and also it has LED illumination and a sound alarm.
I first thought that maybe the battery is the key. Model AW-80-1AV runs on CR2025. Energizer CR2025 datasheet specifies that this battery has nominal output voltage of 3 volts and nominal capacity of 163 mAh, so it stores 0,489 volt-ampere-hours of energy.
For comparison, typical basic model of Swatch run about three years on Renata silver oxide 390 (SR1130SW) battery that has nominal output voltage of 1,55 volts and nominal capacity of 60 mAh and so stores 0,093 volt-ampere-hours of energy.
So CR2025 stores about five times more energy, but the basic model of Swatch only has hands - no digital display, no illumination, no alarm, so it likely consumes less energy.
There clearly must be something more than a bigger battery that makes 10 years battery life possible.
How is 10 years battery life possible in a rather energy consuming wristwatch?